/*
 * Copyright (C) 2012-2016 Markus Junginger, greenrobot (http://greenrobot.org)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.greenrobot.eventbus;

final class PendingPostQueue {
  private PendingPost head;
  private PendingPost tail;

  synchronized void enqueue(PendingPost pendingPost) {
    if (pendingPost == null) {
      throw new NullPointerException("null cannot be enqueued");
    }
    if (tail != null) {
      tail.next = pendingPost;
      tail = pendingPost;
    } else if (head == null) {
      head = tail = pendingPost;
    } else {
      throw new IllegalStateException("Head present, but no tail");
    }
    notifyAll();
  }

  synchronized PendingPost poll() {
    PendingPost pendingPost = head;
    if (head != null) {
      head = head.next;
      if (head == null) {
        tail = null;
      }
    }
    return pendingPost;
  }

  synchronized PendingPost poll(int maxMillisToWait) throws InterruptedException {
    if (head == null) {
      wait(maxMillisToWait);
    }
    return poll();
  }
}
